Two Ships

[Badger]

There are two ships of equal size and strength.One is made of wood and the other of steel.Can you explain which is heavier ?

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[cameronke]

The wooden one

The modulus of steel is greater than that for wood. Therefore the mass of wood required for the same strength (assuming similar method of construction) will be greater in the same ratio of their respective moduli.

I think!?!

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[cameronke]

oops

forgot to consider the relative density of steel against wood so by my reasoning the weight of the wooden boat will be (density of wood/density of steel) X (modulus of steel/modulus of wood) X weight of steel boat

(Methinks perchance)

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[jimi]

Define size - volume or displacement.
Define strength.

<hr width=100% size=1>.. whit way roon should it be again ..

 

[DeeGee]

The specific strength of wood and steel are about the same (see The New Science of Strong Materials - author slips my memory). So prima facie you would expect them to be about the same weight. However, it is easier to use less wood in places of lowstress, wherease it would be inconvenient to have variable thickness plates - so it should be possible for the wooden ship to be lighter. On the other hand, since it is specific strenght, the wooden ship would have less internal volume due to thicker substance.

<hr width=100% size=1>Black Sugar - the sweetest of all

 

[tcm]

To be of equal size and strength, i think the wooden one would have to be quite well built and reinforced etc, but the steel one made nice and flimsy. So the wooden one would be heavier.

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[Badger]

Wood and steel the same strength ?

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[Badger]

TCM does it again !

The ship made of wood is heavier, since pound for pound steel is much stronger than wood and the wooden ship would require a good deal more material to be of equal strength.

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[boatmike]

If they are the same size they are probably the same displacement assuming same hull shape and ignoring ballast. Assuming this is the case they both weigh the same. The question of strength needs to be defined in more scientific terms. Steel is stronger and heavier than wood as a material but a properly built wooden ship could be equally as strong or stronger in terms of resisting normal forces. A steel hull could deflect (dent) under impact where the wooden one wont. Conversely a really big impact could splinter a wooden hull and let in water where a conventional welded hull will dent and remain watertight. Depends entirely where and how it is impacted. In catastrophic damage the strength of the material used is secondary to the build method. What usually goes first is weld lines on steel and fasteners on wood. Ain't no simple answer!

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[DeeGee]

Re: Wood and steel the same strength ?

Specific strength. This refers to same weight of wood as steel. So, if we had a plank 4inches wide by 3ft long, it would be that much thicker than a same width and length steel 'plank' of the SAME WEIGHT. This is not my tin-pot theory, this is textbook stuff from years ago when I studied materials science. However, I am NOT an expert, but this is by an expert...

The New Science of Strong Materials: Or Why You Don't Fall Through the Floor (Penguin Science)
J.E. Gordon

<hr width=100% size=1>Black Sugar - the sweetest of all